rrb mechanical engineer solved model paper 7

8/9/2019 RRB Mechanical Engineer Solved Model Paper 7

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1. Unit of thermal conductivity in M.K.S. units is

(a) kcal/kg m2

(!) kcal"m/hr m2

(c) kcal/hr m2

(d) kcal"m/hr

(e) kcal"m/m2 .

#ns$ !

2. Unit of thermal conductivity in S.%. units is

(a) &/m2 sec

(!) &/m K sec

(c) '/m K

(d) (a) and (c) a!ove(e) (!) and (c) a!ove.

#ns$ e

. hermal conductivity of solid metals *ith rise in tem+erature normally

(a) increases

(!) decreases

(c) remains constant

(d) may increase or decrease de+ending on tem+erature

(e) un+redicta!le.

#ns$ !

,. hermal conductivity of non"metallic amor+hous solids *ith decrease in tem+erature

(a) increases

(!) decreases



(e) un+redicta!le.

#ns$ !

-. eat transfer takes +lace as +er "

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(a) eroth la* of thermodynamics

(!) first la* of thermodynamic

(c) second la* of the thermodynamics

(d) Kirchhoff la* (e) Stefan0s la*.

#ns$ c

. 'hen heat is transferred from one +article of hot !ody to another !y actual motion of the heated

+articles it is referred to as heat transfer !y

(a) conduction

(!) convection

(c) radiation

(d) conduction and convection

(e) convection and radiation.

#ns$ a

3. 'hen heat is transferred form hot !ody to cold !ody in a straight line *ithout affecting the

intervening medium it is referred as heat transfer !y

(a) conduction

(!) convection

(c) radiation



#ns$ c

4. Sensi!le heat is the heat re5uired to

(a) change va+our into li5uid

(!) change li5uid into va+our

(c) increase the tem+erature of a li5uid of va+our

(d) convert *ater into steam and su+erheat it

(e) convert saturated steam into dry steam.

#ns$ c

6. he insulation a!ility of an insulator *ith the +resence of moisture *ould

(a) increase

(!) decrease



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(c) remain unaffected

(d) may increase/decrease de+ending on tem+erature and thickness of insulation

(e) none of the a!ove.

#ns$ !

17. 'hen heat is ransferred !y molecular collision it is referred to as heat transfer !y

(a) conduction

(!) convection

(c) radiation

(d) scattering


#ns$ !

11. eat transfer in li5uid and gases takes +lace !y(a) conduction

(!) convection

(c) radiation



#ns$ !

12. 'hich of the follo*ing is the case of heat transfer !y radiation

(a) !last furnace

(!) heating of !uilding

(c) cooling of +arts in furnace

(d) heat received !y a +erson from fire+lace

(e) all of the a!ove.

#ns$ d

1. eat is closely related *ith

(a) li5uids

(!) energy

(c) tem+erature

(d) entro+y

(e) enthal+y.

#ns$ c



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1,. 8ick u+ tne *rong case. eat flo*ing from one side to other de+ends directly on

(a) face area

(!) time

(c) thickness

(d) tem+erature difference

(e) thermal conductivity.

#ns$ c

1-. Metals are good conductors of heat !ecause

(a) their atoms collide fre5uently

(!) thier atoms"are relatively far a+art

(c) they contain free electrons

(d) they have high density

(e) all of the a!ove.#ns$ a

1. 'hich of the follo*ing is a case of steady state heat transfer

(a) %.. engine

(!) air +reheaters

(c) heating of !uilding in *inter

(d) all of the a!ove


#ns$ e

13. otal heat is the heat re5uired to

(a) change va+our into li5uid

(!) change li5uid into va+our

(c) increase the tem+erature of a li5uid or va+our

(d) convert *ater into steam and su+erheat it

(e) convert saturated steam into dry steam.

#ns$ d

14. ork is a good insulator !ecause it has

(a) free electrons

(!) atoms colliding fre5uency

(c) lo* density

(d) +orous !ody



5/21


#ns$ d

16. hermal conductivity of *ater in general *ith rise in tem+erature

(a) increases

(!) decreases




#ns$ d

27. hermal conductivity of *ater at 27 is of the order of

(a) 7.1

(!) 7.2(c) 7.,2

(d) 7.-1

(e) 7.,.

#ns$ d

21. em+erature of steam at around -,7 can!e measured !y

(a) thermometer

(!) radiatiouv +yrometer

(c) thermistor

(d) thermocou+le

(e) thermo+ile.

#ns$ d

22. hermal conductivity of air at room tem+erature in kcal/m hr is of the order of

(a) 7.772

(!) 7.72

(c) 7.71

(d) 7.1

(e) 7.-.

#ns$ !

2. he time constant of a thermocou+le is

(a) the time taken to attain the final tem+erature to !e measured



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(!) the time taken to attain -79 of the value of initial tem+erature difference

(c) the time taken to attain .29 of the value of initial tem+erature difference

(d) determined !y the time taken to reach 177 from 7


#ns$ c

2,. hermal conductivity of air *ith rise in tem+erature

(a) increases

(!) decreases




#ns$ a

2-. eat flo*s from one !ody to other *hen they have

(a) different heat contents

(!) different s+ecific heat

(c) different atomic structure

(d) different tem+eratures


#ns$ d

2. he conce+t of overall coefficient of heat transfer is used in heat transfer +ro!lems of

(a) conduction

(!) convection

(c) radiation

(d) all the three com!ined

(e) conduction and comte:ction.

#ns$ e

23. %n heat transfer conductance e5uals conductivity (kcal/hr/s5m//cm) divided !y

(a) hr (time)

(!) s5m (area)

(c) (tem+erature)

(d) cm (thickness)

(e) kcal (heat).

#ns$ d



7/21

24. he amount of heat flo* through a !ody !y conduction is

(a) directly +ro+ortional to the surface area of the !ody

(!) directly +ro+ortional to the tem+erature difference on the t*o faces of the !ody

(c) de+endent u+on the material of the !ody

(d) inversely +ro+ortional to the thickness of the !ody


#ns$ e

26. 'hich of the follo*ing has least value of conductivity

(a) glass

(!) *ater

(c) +lastic

(d) ru!!er(e) air.

#ns$ e

7. 'hich of the follo*ing is e;+ected to have highest thermal conductivity

(a) steam

(!) solid ice

(c) melting ice

(d) *ater

(e) !oiling *ater.

#ns$ !

1. hermal conductivity of glass"*ool varies from sam+le to sam+le !ecause of variation in

(a) com+osition

(!) density

(c) +orosity

(d) structure


#ns$ e

2. hermal conductivity of a material may !e defined as the

(a) 5uantity of heat flo*ing in one second through one cm cu!e of material *hen o++osite faces


8/21

thickness 1 cm *hen its faces differ in tem+erature !y 1

(c) heat conducted in unit time across unit area through unit thickness *hen a tem+erature

difference of unity is maintained !et*een o++osite faces



#ns$ d

. 'hich of the follo*ing has ma;imum value of thermal conductivity

(a) aluminium

(!) steel

(c) !rass

(d) co++er

(e) lead.

#ns$ a

,. Moisture *ould find its *ay into insulation !y va+our +ressure unless it is +revented !y

(a) high thickness of insulation

(!) high va+our +ressure

(c) less thermal conductivity insulator

(d) a va+our seal


#ns$ d

-. eat is transferred !y all three modes of transfer vi conduction convection and radiation in

(a) electric heater

(!) steam condenser

(c) melting of ice

(d) refrigerator condenser coils

(e) !oiler.

#ns$ e

. #ccording to 8revost theory of heat e;change

(a) it is im+ossi!le to transfer heat from lo* tem+erature source to t high tem+erature source

(!) heat transfer !y radiation re5uires no medium

(c) all !odies a!ove a!solute ero emit radiation

(d) heat transfer in most of the cases takes +lace !y com!ination of conduction convection and

radiation



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(e) rate of heat transfer de+ends on thermal conductivity and tem+erature difference.

#ns$ c

3. he ratio of heat flo* =1/=2 from t*o *alls of same thickness having their thermal

conductivities as #> " 2K2 *ill !e

(a) %

(!) 7.-

(c) 2

(d) 7.2-

(e) ,.7

#ns$ c

4. eat transfer !y radiation mainly de+ends u+on

(a) its tem+erature(!) nature of the !ody

(c) kind and e;tent of its surface



#ns$ d

6. hermal diffusivity is

(a) a dimensionless +arameter

(!) function of tem+erature

(c) used as mathematical model

(d) a +hysical +ro+erty of the material

(e) useful in case of heat transfer !y radiation.

#ns$ d

,7. hermal diffusivity of a su!stance is .

(a) +ro+ortional of thermal conductivity

(!) inversely +ro+ortional to k

(c) +ro+ortional to (kf

(d) inversely +ro+ortional to k2


#ns$ a

,1. Unit of thermal diffusivity is



10/21

(a) m2/hr

(!) m2/hr

(c) kcal/m2 hr

(d) kcal/m.hr

(e) kcal/m2 hr.

#ns$ a

,. hermal conductivity of *ood de+ends on

(a) moisture

(!) density

(c) tem+erature



#ns$ d

,,. %n convection heat transfer from hot flue gases to *ater tu!e even though flo* may !e

tur!ulent a laminar flo* region (!oundary layer of film) e;ists close to the tu!e. he heat transfer

through this film takes +lace !y

(a) convection

(!) radiation

(c) conduction

(d) !oth convection and conduction


#ns$ c

,-. ?ilm coefficient is defined as %nside diameter of tu!e

(a) @5uivalent thickness of film

(!) hermal conductivity @5uivalent thickness of film S+ecific heat ; Aiscosity

(c) hermal conductivity Molecular diffusivity of momentum hermal diffusivity

(d) ?ilm coefficient ; %nside diameter hermal conductivity


#ns$ !

,. eat conducted through unit area and unit thick face +er unit time *hen tem+erature

difference !et*een o++osite faces is unityis called

(a) thermal resistance

(!) thermal coefficient



11/21

(c) tem+erature gradient

(d) thermal conductivity

(e) heat"transfer.

#ns$ d

,6. he rate of energy emission from unit surface area through unit solid angle along a normal to

the surface is kno*n as

(a) emissivity

(!) transmissive

(c) reflectivity

(d) intensity of radiation

(e) a!sor+tivity.

#ns$ d

-7. @missivity of a *hite +olished !ody in com+arison to a !lack !ody is

(a) higher

(!) lo*er

(c) same

(d) de+ends u+on the sha+e of !ody


#ns$ !

-1. # grey !ody is one *hose a!sor+tivity

(a) varies *ith tem+erature

(!) varies *ith *avelength of the incident ray

(c) is e5ual to its emissivity

(d) does not vary *ith tem+erature and. *avelength of the incident ray


#ns$ c

-. *o !alls of same material and finish have their diameters in the ratio of 2 $ 1 and !oth are

heated to same tem+erature and allo*ed to cool !y radiation. Bate of cooling !y !ig !all as com+ared

to smaller one *ill !e in the ratio of

(a) 1 $1

(!) 2$ 1

(c) 1 $ 2

(d) , $ 1



12/21

(e) 1 $ ,.

#ns$ c

--. # non"dimensional num!er generally associated *ith natural convection heat transfer is

(a) Crashoff num!er

(!) Dusselt num!er

(c) 'e!er num!er

(d) 8randtl num!er

(e) Beynold num!er.

#ns$ a

-. EMF in case of counter flo* heat e;changer as com+ared"to +arallel flo* heat e;changer is

(a) higher

(!) lo*er(c) same

(d) de+ends on the area of heat e;changer

(e) de+ends on tem+erature conditions.

#ns$ a

-3. %n heat e;changers degree of a++roach is defined as the difference !et*een tem+eratures of

(a) cold *ater inlet and outlet

(!) hot medium inlet and outlet

(c) hot medium outlet and cold *ater inlet

(d) hot medium outlet and cold *ater outlet


#ns$ d

-4. %n counter flo* heat e;changers

(a) !oth the fluids at inlet (of heat e;changer *here hot fluid enters) are in their coldest state

(!) !oth the fluids at inlet are in their hottest state

(c) !oth the fluids .at e;it are in their hottest state

(d) one fluid is in hottest state and other in coldest state at inlet

(e) any com!ination is +ossi!le de+ending on design of heat e;changer.

#ns$ !

-6. # steam +i+e is to !e insulated !y t*o insulating materials +ut over each other. ?or !est results

(a) !etter insulation should !e +ut over +i+e and !etter one over it



13/21

(!) inferior insulation should !e +ut over +i+e and !etter one over it

(c) !oth may !e +ut in any order

(d) *hether to +ut inferior G%E over +i+e or the !etter one *ould de+end on steam tem+erature

(e) un+redicta!le.

#ns$ a

1. ?ourier0s la* of heat conduction is valid for

(a) one dimensional cases only

(!) t*o dimensional cases only

(c) three dimensional cases only

(d) regular surfaces having non"uniform tem+erature gradients

(e) irregular surfaces.

#ns$ a

2. #ccording of Kirchhoff la*

(a) radiant heat is +ro+ortional to fourth +o*er of a!solute tem+erature

(!) emissive +o*er de+ends on tem+erature

(c) emissive +o*er and a!sor+tivity are constant for all !odies

(d) ratio of emissive +o*er to a!sor+tive +o*er is ma;imum for +erfectly !lack !ody

(e) ratio of emissive +o*er to a!sor+tive +o*er for all !odies is same and is e5ual to the emissive

+o*er of a +erfectly !lack !ody.

#ns$ e

. #ll radiations in a !lack !ody are

(a) reflected

(!) refracted

(c) transmitted

(d) a!sor!ed

(e) +artly reflected and +artly a!sor!ed.

#ns$ d

,. #ccording to Kirchoff0s la* the ratio of emissive +o*er to a!sor+tivity for all !odies is e5ual to

the emissive +o*er of a

(a) grey !ody

(!) !rilliant *hite +olished !ody

(c) red hot !ody

(d) !lack !ody



14/21


#ns$ d

-. he conce+t of overall coefficient of heat transfer is used in case of heat transfer !y

(a) conduction

(!) convection

(c) radiation



#ns$ d

. he unit of overall coefficient of heat transfer is

(a) kcal/m2

(!) kcal/hr (c) kcal/m2 hr

(,) kacl/m hr

(e) kcal/m hr .

#ns$ c

4. &oule sec is the unit of

(a) universal gas constant

(!) kinematic viscosity

(c) thermal conductivity

(d) 8lanck0s constant


#ns$ d

6. he value of 8ortland num!er for air is a!out

(a) 7.1

(!) 7.

(c) 7.3

(d) 1.3

(e) 17.-.

#ns$ c

37. he value of the *avelength for ma;imum emissive +o*er is given !y

(a) 'ien0s la*



15/21

(!) 8lanck0s la*

(c) Stefan0s la*

(d) ?ourier0s la*

(e) Kirchhoff0s la*.

#ns$ a

32. Eog mean tem+erature difference in case of counter flo* com+ared to +arallel flo* *ill !e

(a) same

(!) more

(c) less

(d) de+ends on other factors


#ns$ !

3. he energy distri!ution of an ideal reflector at higher tem+eratures is largely in the range of

(a) shorter *avelength

(!) longer *avelength

(c) remains same at all *avelengths

(d) *avelength has nothing to do *ith it


#ns$ a

3,. otal emissivity of +olished silver com+ared to !lack !ody is

(a) same

(!) higher

(c) more or less same

(d) very much lo*er

(e) very much higher.

#ns$ d

3-. #ccording to Stefan"Holtmann la* ideal radiators emit radiant energy at a rate +ro+ortional

to

(a) a!solute tem+erature

(!) s5uare of tem+erature

(c) fourth +o*er of a!solute tem+erature

(d) fourth +o*er of tem+erature

(e) cu!e of a!solute tem+erature.



16/21

#ns$ c

3. 'hich of the follo*ing +ro+erty of air does not increase *ith rise in tem+erature

(a) thermal conductivity

(!) thermal diffusivity

(c) density

(d) dynamic viscosity

(e) kuiematic viscosity.

#ns$ c

33. he unit of Stefan Holtmann constant is

(a) *att/cm2 K

(!) *att/cm, K

(c) *att2/cm K,(d) *att/cm2 K,

(e) *att/cm2 K2.

#ns$ d

34. %n free con"vection heat transfer Dusselt num!er is function of

(a) Crashoff no. and Beynold no.

(!) Crashoff no. and 8randtl no.

(c) 8randtl no. and Beynold no.

(d) Crashoff no. 8randtl no. and Beynold no.


#ns$ !

36. Stefan Holtmann la* is a++lica!le for heat transfer !y

(a) conduction

(!) convection

(c) radiation

(d) conduction and radiation com!ined

(e) convection and radiation com!ined.

#ns$ c

47. he thermal diffusivities for gases are generally

(a) more than those for li5uids

(!) less than those for li5uids



17/21

(c) more than those for solids

(d) de+endent on the viscosity

(e) same as for the li5uids.

#ns$ a

41. he thermal diffusivities for solids are generally

(a) less than those for gases

(!) >ess than those for li5uids

(c) more than those for li5uids and gases

(d) more or less same as for li5uids and gases

(e) erci.

#ns$ c

4. hermal diffusivity of a su!stance is(a) directly +ro+ortional to thermal conductivity

(!) inversely +ro+ortional to density of su!stance

(c) inversely +ro+ortional to s+ecific heat



#ns$ d

4-. he ratio of the emissive +o*er and a!sor+tive +o*er of all !odies is the same and is e5ual to

the emissive +o*er of a +erfectly !lack !ody. his statement is kno*n as

(a) Krichoff0s la*

(!) Stefan0s la*

(c) 'ien0 la*

(d) 8lanck0s la*

(e) Hlack !ody la*.

#ns$ a

4. #ccording to Stefan0s la* the total radiation from a !lack !ody +er second +er unit area is

+ro+ortional to

(a) a!solute tem+erature

(!) 2

(c) -

(d) t

(e) l/.



18/21

#ns$ d

43. #ccording to 'ien0s la* the *avelength corres+onding to ma;imum energy is +ro+ortion to

(a) a!solute tem+erature ()

(!) %2

(c) f

(d) t

(e) 1/r.

#ns$ a

44. Fe+ending on the radiating +ro+erties a !ody *ill !e *hite *hen

(a) + I 7 ; I 7 and a I 1

(!) +Il I 7anda I 7

(c) + I 7 ; I 1 and a I 7(d) ; I 7 a J + I 1

(e) a I 7 ; J + I 1.

*here a I a!sor+tivity + I reflectivity ; I transmissivity

#ns$ !

46. Fe+ending on the radiating +ro+erties a !ody *ill !e !lack *hen

(a) + I 7 ; I 7 and a I 1

(!) +I l I 7anda I 7

(c) + I 7 ; I 1 and a I 7

(d) ; I 7 a J + I 7

(e) a I 7; J +I 1.

*here a I a!sor+tivity + II reflectivity I transmissivity.

#ns$ a

67. Fe+ending on the radiating +ro+erties a !ody *ill !e o+a5ue *hen

(a) + I 7 ; I 7 and a I 1

(!) +Il; I 7anda I 7

(c) + I 7 ; I 1 and a I 7

(d) ; " 7 a J + I 1

(e) aI7; J +I 1.

*here a I a!sor+tivity + I reflectivity I transmissivity.

#ns$ d



19/21

61. he total emissivity +o*er is .defined as the total amount of radiation emitted !y a !lack !ody +er

unit

(a) tem+erature

(!) thickness

(c) area

(d) time

(e) area and time.

#ns$ d

62. he ratio of the energy a!sor!ed !y the !ody to total energy falling on it is called

(a) a!sor+tive +o*er

(!) emissive +o*er

(c) a!sor+tivity

(d) emissivity(e) none of the a!ove.

#ns$ a

6. ,79 of incident radiant energy on the surface of a thermally trans+arent !ody is reflected !ack.

%f the transmissivity of the !ody !e 7.1- then the emissivity of surface is

(a) 7.,-

(!) 7.--

(c) 7.,7

(d) 7.3-

(e) 7.7.

#ns$ a

6,. he amount of radiation mainly de+ends on

(a) nature of !ody

(!) tem+erature of !ody

(c) ty+e of surface of !ody



#ns$ d

6-. he emissive +o*er of a !ody de+ends u+on its

(a) tem+erature

(!) *ave length



20/21

(c) +hysical nature



#ns$ d

6. *o +lates s+aced 1-7 mm a+art are maintained at 1777 and 37. he heat transfer *ill

take +lace mainly !y

(a) convection

(!) free convection

(c) forced convection

(d) radiation

(e) radiation and convection.

#ns$ d

63. #!sor+tivity of a !ody *ill !e e5ual to its emissivity

(a) at all tem+eratures

(!) at one +articular tem+erature

(c) *hen system is under thermal e5ui+li!rium

(d) at critical tem+erature

(e) for a +olished !ody.

#ns$ c

64. %n re generator ty+e heat e;changer heat transfer takes +lace !y

(a) direct mi;ing of hot and cold fluids

(!) a com+lete se+aration !et*een hot and cold fluids

(c) flo* of hot and cold fluids alternately over a surface

(d) generation of heat again and again

(e) indirect transfer.

#ns$ c

66. # +erfect !lack !ody is one *hich

(a) is !lack in colour

(!) reflects all heat

(c) transmits all heat radiations

(d) a!sl+r!s heat radiations of all *ave lengths falling on it

(e) fully o+a5ue.

#ns$ d



21/21

177. 8lanck0s la* holds good for

(a) !lack !odies

(!) +olished !odies

(c) all colored !odies



#ns$ a

171. %f the tem+erature of a solid surface changes form 23 to 23 then its emissive +o*er

changes in the ratio of

(a)

(!)

(c) 6(d) 23

(e) 41.

#ns$ e

172. Fe+ending on the radiating +ro+erties !ody *ill !e trans+arent *hen

(a) + I 7 ; I 7 and a I 1

(!) +Il; I 7 and a I 7

(c) + I 7 I l and a I 7

(d) I 7 a J + I 1

(e) a I 7; J +I 1.

#ns$ c

17. # grey !ody is one *hose a!sor+tivity

(a) varies *ith tem+erature

(!) varies *ith the *ave length of incident ray

(c) varies *ith !oth

(d) does not vary *ith tem+erature and *ave length of the incident ray

(e) there is no such criterion.

#ns$ d


rrb mechanical engineer solved model paper 7

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